(1) Field of the Invention
The present invention relates to a ceramic thick film circuit substrate useful for an electronic components, and more particularly to a hybrid integrated circuit.
(2) Description of the Prior Art
As shown in FIG. 1 as the conventional hybrid integrated circuit substrates there has been known a ceramic thick-film circuit substrate 7 in which a ceramic multilayer substrate 5 is constituted by alternately forming a conductive layer 2 consisting of a metal having a high melting point, such as tungsten, molybdenum or the like and a dielectric layer 3 with via-holes and a thick-film circuit 6 consisting of a conductor, resistor and the like which connect to the conductive layer 2, is formed thereon.
In such a ceramic thick film circuit substrate 7, silver paste has been employed as a material for forming the thick film circuit for the reason of electrical characteristics such as conductivity and specific resistance, the adhesion to the ceramic multilayer substrate and the like, and the thick film circuit is formed by firing at a temperature of more than 600.degree. C. in an oxidizing atmosphere. Therefore, such a circuit substrate has the drawbacks that the conductive of the metal having high melting point where it is coated with no dielectric layer is likely to undergo oxidation, so that the resistance between the conductive layer and the thick film circuit will increase.
To eliminate these problems, it has been proposed to apply gold-plating on the conductive layer of the ceramic multilayer substrate, but it has been difficult to assuredly obtain a ceramic thick film circuit substrate which can completely prevent the oxidation of the metal having the high melting point and this has further problems in economy.
The present invention has been contrived to solve the above-mentioned problems of the prior art.